Intrinsically conducting polymers are of wide utility in applications such as electronic packaging, organic light-emitting diodes (LEDs), electrochromic windows and displays, volatile organic gas sensors, and the like. Intrinsically conducting polymers of particular interest possess a relatively low band gap (Eg), which refers to the energy difference between two electronic energy levels (the conduction band and the valence band). The band gap exhibited by a given polymer depends upon a variety of factors, including the structure of the monomer(s) used to form the polymer. For example, intrinsically conductive polymers formed from thiophene and substituted thiophene monomers are known. Poly(thiophene) has a band gap of 2.1 electron volts (eV), poly(3,4-ethylenedioxythiophene) (a.k.a. PEDOT) has a band gap of 1.7 eV, poly(2-decylthieno[3,4-b]thiophene) has a band gap of 0.92 eV, and poly(2-phenylthieno[3,4-b]thiophene) has a band gap of 0.85 eV. Intrinsically conductive polymers comprising polymerized units of thieno[2,3-b]thiophene, thieno[3,2-b]thiophene and other fused and substituted thiophenes are also known.
There are a number of drawbacks associated with many of the currently available processes of making these intrinsically conducting polymers. For example, one current process of making conductive PEDOT polymers, which are widely used for making capacitors, is via a dipping process of the tantalum/tantalum oxide substrates into a bath containing the monomer 3,4-ethylenedioxythiophene (a.k.a. EDOT) and ferric chloride. The bath life is only 48 hrs since EDOT is unstable in the presence of ferric chloride, the yields are low, less than 30%, and generally, PEDOT will deposit on all surfaces including the capacitors, the bath walls, etc.
There remains a continuing need in the art for more stable starting materials that can be converted directly into a conductive polymer. Furthermore, there is a need for an improved process of making conductive polymers that is more convenient and efficient, and that would provide higher molecular weight products with better mechanical properties.